Polyphenylene ether resins (hereinafter “PPE”) are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Furthermore, the combination of PPE with other resins provides blends that result in additional overall properties such as chemical resistance, high strength, and high flow.
One technical obstacle to the development of such blends is the lack of compatibility between PPE and many resins. This lack of compatibility manifests itself often through very poor physical properties as well as delamination in molded parts. Methods have been developed to improve the PPE compatibility with many resins such as, for example, with polyesters and polyamides. One of the more effective methods involves functionalizing PPE to make functionalized PPE containing moieties such as acid, anhydride, epoxy, orthoester, and the like that are reactive with the other resin in the blend. It is believed that when the functionalized PPE is allowed to react with the other resin that relatively small amounts of copolymer between the resins are formed. The copolymer is believed to be in large part responsible for improved compatibility between the PPE and the other resin. Indications of improved compatibility include resistance to delamination, improved physical properties such as increased tensile and impact properties and a stabilized morphology between the blend component phases under static and/or low shear conditions.
Methods to prepare functionalized PPE have included solution functionalization with an acid halide containing compound, such as trimellitic anhydride acid chloride, to make an endcapped PPE containing at least one reactive moiety such as acid, anhydride, epoxy, orthoester, and the like. This method is rather limited in the variety of functionalized PPE that can be made. Also, the by-products from the capping reaction tend to cause emulsion and/or isolation issues in the solvent precipitation stage of the process.
Another known method to prepare functionalized PPE related to melt functionalization of the PPE in an extruder. This method involved melting and mixing PPE with a functionalizing agent to result in a functionalized PPE. The functionalizing agent is typically a compound containing a carbon-carbon double or triple bond and one of the aforementioned reactive moieties and is believed to react through the unsaturated bond to functionalize the PPE. Additional polymers could be fed into the same extruder or alternatively, the functionalized PPE could be isolated and subsequently used to prepare other compositions. Melt functionalization has issues, such as difficulty in feeding PPE into the extruder due to low bulk density and wide particle size distribution. Moreover, PPE are often powders and require special handling to avoid potential dust explosion.
As explained above, the methods known in the art teach functionalization of the PPE with reactive groups such as acid, anhydride, epoxy, orthoester, and the like. However, for blending PPE with resin systems that involve curing or polymerization reactions, including radical reactions, it would be highly desirable to have a PPE that contained residual aliphatic unsaturation and capped phenolic end groups at the same time. Incorporation of unsaturated species onto the PPE to result in an olefinic functionalized PPE may allow for chemical grafting to occur between the olefinic functionalized PPE and the other unsaturated species that are being polymerized. Moreover, the hydroxyl groups that exist on PPE may interfere with radical polymerization reactions of unsaturated monomers and lead to undesirable low polymerization rates of the unsaturated monomer species.
PPE known in the art typically are of fairly high molecular weight for blending in the melt phase with other polymers and generally have in excess of 50 repeat monomer units, most often in excess of 80 or more repeat monomer units. Consequently, functionalization reactions and isolation methods have been developed for high molecular weight PPE. Although many physical properties, such as tensile properties, are enhanced with the high molecular weight of the PPE in the polymeric blend, in other new resin blend compositions, such as, for example, the polymerization of vinyl-substituted aromatic monomers, the high viscosity of the PPE having more than 50 repeat monomer units is undesirable as it presents difficulty with mixing. Additionally, the overall number of available endgroups available for chemical modification becomes fairly limited as the molecular weight increases.
For blending PPE with resin systems that involve curing or polymerization reactions, including radical reactions, it would be highly desirable from the standpoints of low viscosity for mixing and a high endgroup number for functionalization to have a PPE that contained residual aliphatic unsaturation and that has less than 50 repeat monomer units on average, preferably less than about 35 repeat monomer units on average. It is therefore apparent that a need continues to exist for novel and improved methods to prepare functionalized PPE containing residual aliphatic unsaturation, especially low molecular weight PPE (i.e. PPE having an intrinsic viscosity less than about 0.30 dl/g as measured in chloroform at 30° C.).